Applications Note AN36
Issue1 - JULY 2002
Another hazard with the excessive voltages
from the blocking diodes is that it can cause
this energy to be dissipated within the Zener
clamping arrangement. As this energy would
normally have been returned to the supply for
reuse it seems appropriate to attempt to save
the energy for reuse within the fan itself. This
is achieved with the Capacitor C5 in Figure 17.
Care needs to be taken with the selection of
the capacitor type and value for each
application. For multilayer chip capacitors it
will be a cost verses value issue and for
electrolytic capacitors a size verses value
issue. In both cases the voltage tolerance of
the chosen part needs careful consideration
as the capacitor needs to reliably withstand
the peak voltages.
Figure 12
Winding Supply with 4.7F Capacitor
APPLICATION CIRCUIT EXAMPLES
When used, the capacitor gives considerable
efficiency improvements with noted
reductions in supply current and driver
device temperature. Figure 11 shows the
winding supply at the winding common point
and shows the voltage being clamped by the
driver active clamping. Figure 12 shows the
effects of adding a 4.7F multilayer ceramic
capacitor (C5 in Figure 17).
In this section are shown complete circuit
examples developed using the ZXBM2001
together with the type of fan it was developed
for. Examples are given for a variety of
applications with the intention that these
circuits will form the starting point for a users
future development in conjunction with the
guidelines given in the previous section.
Figure 11
Winding Supply
AN 36 - 9
ZETEX [ ZETEX SEMICONDUCTORS ]
